Daca notam latura opusa ∡A cu "a", a lui ∡B cu b, si "a" lui ∡C cu "c", teorema sinusurilor
este: [tex] \frac{a}{sinA}= \frac{b}{sinB}= \frac{c}{sinC}=2R,unde,R=raza.cerc.circumscris,vom avea: [/tex][tex] \frac{a}{sinA}= \frac{9}{sin120}= \frac{9}{ \frac{ \sqrt{3} }{2} }= \frac{9*2* \sqrt{3} }{ \sqrt{3}* \sqrt{3} }=6 \sqrt{3}=2R,deci,R=3 \sqrt{3} [/tex]
